Conventional torque transmission shafts (torque transmission devices) used as propeller shafts (drive shafts) of vehicles are disclosed, for example, in Patent Documents 1 and 2. The torque transmission shafts include a cylinder made of fiber reinforced plastics (FRP) and end joints made of metal and coupled to both ends of the cylinder. The FRP cylinder provides the advantage of achieving weight reduction while ensuring the necessary strength and durability.
The torque transmission device disclosed in Patent Document 2 includes an FRP cylindrical member and outer collars. The FRP cylindrical member is fitted to a region of a serrated portion formed on the outer circumferential surface of each of end joints. The outer collars connect the end joints to the cylindrical member. The outer collars each include a larger diameter portion and a smaller diameter portion. The larger diameter portion of the outer collar is coupled to the outer circumferential surface of the cylindrical member, and the smaller diameter portion of the outer collar is coupled to the serrated portion of the end joint.
That is, the securement between the end joints and the FRP cylindrical member and the securement between the end joints and the outer collars are both provided by the serrated portions of the end joints. This configuration eliminates the need to form, in each end joint, a special securement portion (for example, a non-circular cross sectional shaft portion included in the drive shaft disclosed in Patent Document 1), and as a result, simplifies the process for forming the end joints.